In providing electrical circuits to a facility, such as a home, one or more branch circuits are wired to distribute electrical power to load devices, such as light fixtures or outlet receptacles. Typically, the receptacle or fixture is hardwired directly to the branch circuit, with power to the device being turned on or off at the device itself. For example, a light fixture might include a pull cord for actuating a switch, while a small appliance might include a power switch.
With recent technological developments it is both possible and advantageous to provide automated control of load devices to provide, for example, remote or timed switching. One such system directs all communication functions into a master system controller. This gives a homeowner flexible communication and power control from anywhere in the home there is a control panel or switch, or even anywhere there is a telephone, such as the car or office. An intelligent outlet receptacle or fixture block allows individual appliances or fixtures to be separately and automatically controlled as necessary or desired. To do so, some means must be provided for controlling switching of power to the load device. To be practical, the switching must be done inexpensively and accurately. A latching relay has been found to be readily adaptable to such an application. A latching relay is latched when connected to a positive polarity voltage source and unlatched when connected to a negative polarity voltage source.
A latching relay includes a relay coil and an electrical contact switched by the relay coil. The relay contact is connected between an AC power source and the load device. Opening and closing of the contact can produce arcing if the transition occurs at a non-zero point on the AC input waveform. This requires that a larger capacity relay be used, increasing expenses and size, to withstand these conditions. Therefore, a desire exists to avoid arcing so that a smaller relay can be used. A known procedure for minimizing arcing is to synchronize the switching of the contact to the AC line input. Particularly, the relay is controlled to lead energization of the relay so that the expected contact switching time occurs at or close to a zero crossing of the AC input.
Without any synchronization the switching occurs randomly. Thus, arcing may or may not occur. While this situation is undesirable, a worse situation exists if a synchronization circuit is not properly timed. As a result, arcing will always occur. Therefore, it is desirable that a synchronization scheme be used which provides adequate time and adjustability to ensure that switching occurs at or near a zero crossing.
The present invention is intended to overcome one or more of the problems discussed above in a novel and simple manner.